Photoshop Tutorials - Color Balance. Channel Mixer
Channel Mixer command allows changing the color channel image by mixing the current color channels. As the result you can get a gray scale image (the image will be based on single color channel), by adding certain percentage of other color channels. Such image can be easily rendered.
This command is available only when you have the composite channel activated in the Channels palette and only for RGB and CMYK color models. In the Output Channel dropdown menu, there are names of the color channels of the current image, and choosing one of them determines the basic channel.
In Source Channels section of the window, there are sliders for each color channel. Moving the slider to the left reduces the contribution of respective channel to the resulting image, and moving to the right increases the contribution.
The range of possible changes varies from -200 to +200 percents. The negative value inverts the image adding a certain percentage of the image negative. The Constant slider adds a certain percentage of opacity for the channel, negative values represent the black channel while the positive values present the white channel.
Monochrome checkbox sets same brightness for all color channels creating the gray scale image. This can be very useful for working with color images that need to be turned to gray scale preserving best quality.
You can also make channels trade places. You can make blue colors in the image become green just by making the blue and green channels trade places. To do so you need select Blue as an output channel from the dropdown menu, then increase the Green value to 100% value and decrease the blue value to 0% value. After that, you select the Green channel form the dropdown menu, reduce Green from 100% to 0% and increase the Blue from 0% to 100% values.
By doing this you will make the blue and green channels trade places.